Flexible sheet-like magnetic discs having a nominal standardized size of about 3.5 inches (so-called "microdiscs") are widely used in a variety of data storage/retrieval systems. For example, cassettes which include flexible magnetic discs are used in conjunction with personal computers so as to load data and/or programs into the central processing unit of the computer, as well as to store data in an off-site location in a more convenient manner.
When placed into service in a magnetic recording/reproducing apparatus, the magnetic disc (which is accommodated for rotational movement within the interior of the cassette case) is caused to spin relative to a magnetic read/write head by means of a motor-driven spindle coacting with an aperture in the central hub of the magnetic disc. The spindle, moreover, serves to center the magnetic disc relative to the magnetic read/write head so that accurate placement and retrieval of data onto and from the disc will ensue.
The motor-driven spindle and the aperture defined in the central hub of the magnetic disc typically coact with one another with close (but not ultrafine) tolerances. As a result, some "play" between the spindle and the aperture might be present which could translate into imprecise and/or varying rotational speed of the flexible magnetic disc during use.
As one means to counteract this problem, conventional flexible magnetic disc cassettes are provided with drag-inducing structures to impart slight drag against the magnetic disc so as to provide for more positive rotational velocity characteristics of the same during use. Typically, the drag-inducing structures will include a non-woven disc-shaped liner in confronting relationship to one face of the flexible magnetic disc, and a lifter (i.e., usually a relatively stiff polymeric film bent into the form of a leaf spring) located on an interior surface of the cassette case. The lifter serves to bias the liner into wiping contact with the surface of the magnetic disc which the liner confronts. The liner, due to its wiping contact with the surface of the magnetic disc, also serves to remove dust particles that may have accumulated thereon.
As can be appreciated, physical contact between the liner and the surface of the magnetic disc may abrade the magnetic disc surface and thus may, over time, degrade the quality and/or ability of the magnetic disc to magnetically store data. In addition, the separate liner and lifter associated with conventional flexible magnetic discs necessarily increase the manufacturing costs due to the increased labor/handling/assembly which such structures require. It is towards reducing (or eliminating entirely) these problems that the present invention is directed.
According to the present invention, cassette cases which house flexible magnetic discs are provided with integrally molded flexible drag fingers that have a free terminal end and which exert a beneficial frictional drag force against the central hub of the magnetic disc. The free ends of these flexible drag fingers thereby impart a small (but needed) amount of frictional drag against the central hub of the magnetic disc to thus cause the disc to spin more reliably during use in a recording/reproducing apparatus.
Most preferably, the drag fingers contact the central hub of the magnetic disc symmetrically relative to its perimeter. That is, the number and/or location of the drag fingers are such that the contact points between the free ends of the drag fingers and the central hub are substantially equally spaced apart about the periphery of the hub (e.g., substantially equal angular separation between the contact points).
Further aspects and advantages of the present invention will become more clear after careful consideration is given to the following detailed discussion thereof.